This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:
3GPPthird generation partnership projectD2Ddevice to device (sometimes termed machine to machineM2M or peer-to-peer P2P)eNBEUTRAN Node B (evolved Node B)LTE/LTE-Along term evolution/long term evolution-advancedMACmedium access controlMCSmodulation and coding schemeRBradio bearerUEuser equipmentULuplink (UE towards eNB)
Recent research has gone into integrating new network topologies into cellular networks. For example, there is a study item in LTE/LTE-A of 3GPP for deploying a heterogeneous network of macros, micros, picos, femtos and relays in the same spectrum. Extending this a bit further enables heterogeneous local communication directly among devices and machines under supervision of the network, which might include D2D communications, communication in the cluster of devices, a grid or group of local machines communicating so as to perform certain tasks in co-operative way, and an advanced device acting as a gateway for a number of other low-capability devices or machines to access the network. A common theme in these examples is that they each utilize a secondary usage of the cellular network.
FIG. 1 illustrates a non-limiting example of such a heterogeneous network with local connections. There is a cellular base station/eNB 101 and typical UEs 102, 103, 104 operating in the cellular communication mode with the base station 101. In this mode, the links 102d, 103d and 104d carry data as well as control signaling. UEs 105, 106 are in direct communication with one another over a D2D link 105d which carries data. The D2D link 105d is facilitated via control signaling with the base station 101 over control-only links 105c, 106c that carry no data, and so the D2D network is integrated into the cellular network. Either or both of these other UEs 105, 106 may also simultaneously have a traditional cellular link with the base station for traditional cellular data communications, but for simplicity of description assume their links 105c, 106c with the base station 101 carry only control information and no data.
One of the problems in integrating local heterogeneous communication into a cellular network is the dynamic interference fluctuation, with a relatively large standard deviation, at the receiver of a local communication device 105, 106 as compared to the standard deviation of the interference power of the cellular users 102, 103, 104 measured at the eNB 101, when we consider the UL as a resource for the secondary communication 105d. Interference at the local communication devices 105, 106 comprises mainly cellular users 102, 103, 104 in the same and in neighbor cells using the same radio resources (time and frequency). Intra-cell interference can be minimized among cellular 102-104 and secondary 105-106 usage via scheduling by the eNB 101, but inter-cell interference from cellular users in neighbor cells is a significant concern. This concern is more acute for uncoordinated cellular network deployments where one can assume only a small amount of co-operation between neighbor eNBs.
FIG. 2 is histogram of interference power that illustrates a difference in the interference situation of the cellular 102-104 and local 105-106 communication devices, assuming a hexagonal grid layout of omnidirectional cells. Interference power at the eNB 101 is shown as bars 204, interference power at the local/D2D UEs 105-106 is shown at bars 203 when no cellular user 102-104 is using the same resources in the same cell, and at bars 202 when there is a cellular user 102-104 using the same resources in the same cell as the local/D2D device 105-106. Even for the case in which the local/D2D devices 105-106 are given dedicated resources in the cell, shown as the doubled bars 204, the deviation of the interference power is much larger than in the cellular case 206. Additionally, the deviation of the interference increases as a function of distance to the eNB 101 as can be seen in FIG. 3.
Additionally, even though local/D2D devices 105-106 have been assigned resources that are orthogonal to a cellular user 102-104 located close to the local/D2D device, and even if we assume high transmit power due to phase noise and carrier synchronization error (EVM) and inverse fast Fourier transform (IFFT) non-perfect orthogonality at the transmitter, there will be in-band emission over subcarriers other than those the transmitter is using. 3GPP TS 36.101 (v9.3.0, 2010-03) gives minimum requirements for such in-band emissions, defined as the average across 12 sub-carriers and as a function of the RB offset from the edge of the allocated UL transmission bandwidth. The in-band emission is measured as the relative UE output power of any non-allocated RB(s) and the total UE output power of all the allocated RB(s). In equation (0) below the formula is given for calculating the minimum requirements for in-band emissions according to 3GPP TS 36.101. FIG. 4 illustrates the in-band emission requirements for QPSK (quadrature/quaternary phase shift keying) and 16-QAM (quadrature amplitude modulation) modulations.max[−25,(20·log10EVM)−3−10·(ΔRB−1)/NRB)]  (0)
This means that the interference situation depicted in FIGS. 2-3 is further challenged by the leakage power of the cellular communication mode users.
With the above challenging interference environment in mind, consider further that low-capability low-power machines/devices may need to send fixed length MAC packets to each other locally. Thus, effective link adaptation and MCS selection scheme may not be helpful for the channel access scheme. From another perspective, wireless engineering seeks to minimize control signaling overhead such as required feedback signaling between local/D2D devices 105-106 and the supervising cellular network 101 as well as feedback signaling between those local/D2D devices 105-106.